Do we really live longer because of “longevity genes”? Researchers cast doubt

It’s now suggested that people likely to live long tend to find each other (assortative mating). How else to explain this?Researchers found that siblings’ and first cousins’ lifespans were well correlated but also:

But spouses’ lifespans were correlated, too. That could be easily explained by spouses sharing the same household and lifestyle: eating the same healthy diet or puffing on cigarettes together. But the researchers noticed something odd: the lifespans of other relatives related only by marriage also correlated. That can’t be explained by genes, and it can’t be explained by shared environment.

So Ruby and his colleagues started investigating the lifespans of in-laws. They looked at siblings-in-law, and first-cousins-in-law, and then further afield, at relationships like “the sibling of a sibling’s spouse” (your brother’s wife’s sister) and “the spouse of a spouse’s sibling” (your husband’s sister’s husband). Even at these distant relationships, lifespans were correlated—if your spouse’s sibling’s spouse lived to a ripe old age, that means you’re a bit more likely to do the same.Cathleen O’Grady, “Genetics play less of a role in lifespan than we thought” at Ars Technica

They came up with a figure of 7% heritability (which includes both genetic and nongenetic inheritances) based on Ancestry.com, which may not be generalized to the whole human population.

But how and why do people find each other? That would be the next question to study. If the recent finding that religiously affiliated people live “9.45 and 5.64 years longer” holds up, that may provide part of the explanation for how they find each other: The others are already there.

One also wonders whether a tendency in a sibling-inlaw group, such as described by the researchers, to care for aged people also makes a difference.

Anecdotally, many aged people die because they have a fall, a heart attack, or a stroke when they are all alone and are found dead days later. They could have been saved and lived another five years if anyone had found them immediately and administered aid or summoned help. That, of course, won’t happen as much among aged people who live in close communities. If so, we might expect ages at death to be higher.

Selective mating is just another expression of genes. The separated twins studies noted that twins married remarkably similar spouses, often with the same first name.

So it’s still mostly genetic. There’s no possible way to separate the genome variables that tend toward longevity from the variables that tend toward marrying a short red-haired Lydia. Each set of variables arises from the same heritable genes.